The present invention is directed to thermoelectric module assembly. More particularly, the invention provides a method for forming an assembly in series of thermoelectric (TE) unicouples. Merely by way of example, the invention has been applied for sizing and assembling silicon-based thermoelectric unicouples bonded thermally in parallel and electrically in series with silicon-based contact wafers and heat sinks to form a 3D package of thermoelectric modules capable of generating electrical energy from high temperature waste heat. It would be recognized that the invention has a much broader range of applicability without limiting to specific material based TE unicouples, in various fields including but not limited to automobile combustion, industrial hot exhaust, nuclear power plants, and aircraft turbines.
An actual thermoelectric device must transport significant amounts of current from one electrode to another in the case of power generation, where a temperature gradient is applied to the thermoelectric material and the Seebeck effect is employed to drive a gradient in voltage and in turn the flow of electrical current. Conversely, an actual thermoelectric device used for refrigeration must carry an appreciable amount of heat with an applied electric current by way of the Peltier effect. In both of these thermoelectric device configurations, the thermoelectric figure of merit ZT of the thermoelectric material is one indicator of the material's efficiency in either converting heat to electricity (Seebeck effect, or thermopower) or pumping heat with electricity (Peltier effect).
In a thermoelectric device, electrodes must be placed on either ends of a thermoelectric material in order to collect current from it or transmit current through it. These electrodes must be made such that they form low resistance electrical and thermal contact to the thermoelectric material with high ZT value, and furthermore allow each TE “leg,” or single element of either p-type or n-type semiconductor material, to be wired together among other TE legs and external circuitry. A TE unicouple (or simply referred as “unicouple”) is a building block used for assembling an actual thermoelectric device with corresponding electrodes. In particular, the unicouple is a three-dimensional structure comprising a first conductive shunt material coupled on a hot side of a p-type thermoelectric leg and an n-type thermoelectric leg and a second conductive shunt material coupled to a cold side of either one or the p-type thermoelectric leg or the n-type thermoelectric leg.
Many efforts for improving thermoelectrics have been made to search for new advanced thermoelectric materials with high ZT value, to determine optimum unicouple structure associated with the thermoelectric material, and to develop feasible processes for forming the unicouples and assembling them to thermoelectric devices. Conventional high ZT thermoelectric materials such as bismuth telluride (Bi2Te3), either in bulk or nanostructured form or alloy form combined with other materials (Ce, Fe, Sb, etc.), have been used in some thermoelectric applications. However, other than the high cost and complexity of manufacturing these materials, which also have toxic characteristics, the poor high-temperature adaptability of such thermoelectric materials also substantially limits these devices to applications in relatively low temperature environments. This drives efforts in research and development on advanced, low-cost, silicon-based TE unicouples for assembling a thermoelectric module that can be used for wide range of temperatures, especially for waste-heat power generation application at high temperature greater than 600° C. as well as refrigeration application for electronic system.